Bag-making method

ABSTRACT

To provide a bag-making method ensuring excellent liquid tightness at the melt-bonded part between the mouth member and the bag unit. A bag-making method for producing a bag by melt-bonding and thereby integrating a mouth member formed of a preliminarily heated synthetic resin and a bag unit formed of a flexible film, the method comprising a preliminary heating step of softening the synthetic resin of the mouth member at the part to be melt-bonded to the bag unit, melt-bonding part of mouth member, while preventing the synthetic resin of the mouth member at the end part in the bag side, end part of mouth member, from being softened at the preliminary heating step, and a step of inserting the preliminarily heated mouth member into the opening of the bag unit and pressing them by a sealing mold to melt-bond the melt-bonding part of the mouth member to the opening; and a medical container produced by the bag-making method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/479,837, filed Jun. 20, 2003, and Japanese Patent Application No.2002-314252, filed Oct. 29, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bag-making method, more specifically,the present invention relates to a bag-making method of producing a bagby melt-bonding a mouth member formed of a synthetic resin and a bagunit formed of a flexible film to ensure excellent liquid tightness atthe melt-bonded part between the mouth member and the bag unit.Furthermore, the present invention relates to a medical container usedafter filling a transfusion solution or blood in the container producedby the above-described bag-making method.

Priority is claimed on Japanese Patent Application No. 2002-314252,filed Oct. 29, 2002.

2. Description of Related Art

In recent years, a medical container formed by using a synthetic resinis often used in place of a glass-made medical container. The syntheticresin-made medical container includes a container produced by blowmolding and a container produced from a film or a sheet (hereinafter, afilm and a sheet are collectively called a “film”) obtained by inflationmolding or T-die casting. Among these, a container produced from a film(hereinafter referred to as a “film bag”) is increasing, because thefilm bag is thin and uniform in the container thickness and can bereduced in the volume after use, the waste is therefore less generatedand at the transfusion, the discharging rate of liquid content can bekept almost constant until the last. In the film bag, a mouth memberwhich is a hollow cylindrical body formed of a synthetic resin andhaving a three-dimensional shape as shown in FIG. 1 is fixed by heatsealing so as to enable filling or discharging of the content. The mouthmember has a hollow circular or elliptic cross-section in many cases.

In the fixing of the mouth member to the film, a three-dimensionallyshaped member must be fixed to a two-dimensional planar film and asshown in FIG. 2, a gap 22 is sometimes generated between the A-framepart of the film and the melt-bonding part of the mouth member(hereinafter referred to as a “A-frame part gap”) to cause leakage ofthe liquid content. Particularly, in the case of a thick film having afilm thickness of 100 μm or more, the film is deformed in agreement withthe shape of the mouth member at the heat sealing, though this may varydepending on the shape of the mouth member, and the once sealed portionis sometimes separated due to restoring stress of the film. Furthermore,on melt-bonding the mouth member and the film by sandwiching these witha sealing mold, the film is subject to an excess tensile stress so as toagree with the shape of the mouth member and this bears a risk ofthinning the film or forming a hole in the film.

For preventing such deformation or hole formation of film, a method ofstacking a heat-resistant layer on the film by using an adhesive toobtain a laminate film enhanced in the heat resistance is known.However, use of an adhesive is not preferred in the medical fieldbecause the adhesive sometimes dissolves out. Accordingly, variousstudies have been made for the bonding technique of causing nodissolving out of a material and enabling liquid-tight bonding withoutgeneration of a gap between a mouth member and a bag unit comprising asingle-layer or multilayer film.

As the container succeeded in solving the problem of the A-frame partgap, a container obtained by bonding a bag unit and a mouth memberprovided with, as shown in FIG. 3, a thin strip 23 outwardly extendingin the left and right sides of the melt-bonding part has been proposed.

Specific examples of the method for producing a container by bonding acontainer body and a mouth member provided with a thin strip outwardlyextending in the left and right sides of the melt-bonding part include:a method of producing a mouth member having previously provided thereonthin strips by using a preheating jig and then heat-sealing it to atransfusion bag (see, Patent Document 1);

-   -   a method of melting the surface of an opening plug at a        temperature higher by 15 to 80° C. than the melting point of the        material for the opening plug before the opening plug comes into        contact with a film or a sheet, simultaneously forming a        fuse-bonding tab in the width of 0.2 to 3 mm on both sides of        the opening plug, and pressing two sheets of film or sheet to        the opening plug from the symmetrical directions to fuse-bond        the films or sheets to the opening plug (see, Patent Document        2);    -   a method of providing a protruding part on the outer        circumferential face of a hollow cylindrical body at symmetrical        positions dividing the hollow cylindrical body into two in the        perpendicular axial direction, with the joining part to the        hollow cylindrical body being narrowed, heating and softening        the protruding parts and then abutting a sheet to the protruding        parts and hollow cylindrical body in the softened state (see,        Patent Document 3);    -   a method of heat-sealing an inflation tube to a mouth part        having fin-like protrusions formed by a metal mold and thereby        producing a bag (see, Patent Document 4); and    -   a method of, before melt-bonding an opening plug to a film or a        sheet, heating the surface layer at the melt-bonding part of the        opening plug in the temperature range from the softening        temperature of the material for the melt-bonding part of the        opening plug to a temperature 13° C. higher than the melting        point by utilizing radiation heat of a heater at a temperature        of 600 to 800° C., pressing the heated opening plug from both        sides by fin-forming metal molds symmetrical with respect to the        opening plug to form fin-like thin strips on the opening plug,        inserting the opening plug still in the heated state between        films or sheets, and melt-bonding the opening plug to the films        or sheets by a heat-sealing mold (see, Patent Document 5).

These are a method of producing a mouth member having previouslyprovided thereon a thin strip outwardly extending in the left and rightsides of the mouth member at the part to be melt-bonded to a film, andthen bonding the mouth member to a bag unit. Such a method not onlyrequires an excess step for forming a thin strip but also encountersproblems at the formation of the thin strip, such as fluctuation in thesize of thin strip, unevenness in the size between left and right thinstrips and attachment of carbide debris from the thin strip-formingmold. In addition, the previously formed thin strip may be deformed, forexample, may be shrunk, distorted or fallen down. Furthermore, theheating is readily accompanied with deformation of the mouth member dueto release of a residual stress in the melt-bonding part generated atthe injection molding of the mouth member, as a result, the positions ofthe mouth member, bag unit and sealing mold cannot be exactly adjustedat the bonding of the mouth member to the bag unit, resulting inunsatisfactory bonding. Accordingly, improvements for more completelypreventing the generation of a A-frame part gap are being demanded.

Particularly, in the case of a large size mouth member with a diameterexceeding 10 mm, thinning of film and generation of pinhole are liableto more often occur.

Patent Document 1

JP-UM-A-61-194638 (the term “JP-UM-A” as used herein means an“unexamined Japanese published utility model application”)

Patent Document 2

Japanese Patent No. 2,940,987

Patent Document 3

Japanese Patent No. 2,791,387

Patent Document 4

JP-A-4-191033 (the term “JP-A” as used herein means an “unexaminedJapanese patent application”)

Patent Document 5

Japanese Patent No. 3,048,486

Patent Document 6

JP-B-3-5304 (the term “JP-B” as used herein means an “examined Japanesepatent publication”)

SUMMARY OF THE INVENTION

The present invention has been made under these circumstances and a mainobject of the present invention is to provide a bag-making method forobtaining a bag with a mouth member, having excellent liquid tightnessat the melt-bonded part between the mouth member and the bag unit, wherethe mouth member is reduced as much as possible in the deformation ofthe melt-bonding part at the preheating, the number of steps is small,and the generation of the A-frame part gap can be stably prevented.

As a result of extensive investigations on the bag-making method ofproducing a bag by melt-bonding a mouth member and a bag unit andcapable of preventing the generation of A-frame part gap, the presentinventors have found that the mouth member produced by injection moldinghas a residual stress generated at the injection molding, this residualstress is released by the heating at the formation of thin strips on themouth member or at the preliminary heating, thereby causing deformation,and this deformation makes it difficult to exactly determine relativepositions of the mouth member, bag unit and sealing mold and gives riseto generation of harmful local contact or gap between the sealing moldand the bag unit, as a result, uniform and stable sealing can be hardlyattained. Accordingly, it has been found that by suppressing thedeformation of the mouth member, a uniform thin strip can be stablyformed, the generation of A-frame part gap can be prevented and at thesame time, the bag unit in the vicinity of the mouth member can beprevented from thinning of film due to heating at the end part of themouth member. The present invention has been accomplished based on thisfinding.

More specifically, the present invention relate to a bag-making methoddescribed in 1) to 7) below.

That is, the above-described object can be attained by developing:

-   -   1) a bag-making method for producing a bag by melt-bonding and        thereby integrating a mouth member formed of a preliminarily        heated synthetic resin and a bag unit formed of a flexible film,        the method comprising a preliminary heating step of softening        the synthetic resin of the mouth member at the part melt-bonded        to the bag unit, which is a melt-bonding part of mouth member        while preventing the synthetic resin of the mouth member at the        end part in the bag side, which is an end part of mouth member        from being softened at the preliminary heating, and a        melt-bonding step of inserting the preliminarily heated mouth        member into the opening of the bag unit and pressing them by a        sealing mold to melt-bond the melt-bonding part of the mouth        member to the opening;    -   2) the bag-making method as described in 1) above, wherein        radiation heat is used for the preliminary heating;    -   3) the bag-making method as described in 1) above, wherein the        end part of the mouth member has a length of 0.5 mm or more;    -   4) the bag-making method as described in 1) above, wherein the        end part of the mouth member is prevented by heat insulating        means from being heated at the preliminary heating;    -   5) the bag-making method as described in 1) above, wherein in        the melt-bonding step, the melt-bonding is performed not to heat        the mouth member in the region at least 0.5 mm from the        lowermost portion of the end part;    -   6) the bag-making method as described in 1) above, wherein a        mouth member supported by a cylindrical body is inserted into        the opening of a bag unit and the mouth member and the bag unit        are melt-bonded while the bag unit is depressurized; and    -   7) a medical container produced by the bag-making method        described in of 1) above.

According to the bag-making method, the number of steps is small andgeneration of a gap in the A-frame part can be stably prevented, so thatthe bag with a mouth member can be prevented from liquid leakage.Furthermore, the film forming the bag unit can be prevented fromthinning at the distal end of the mouth member due to heating andtherefore, the bag can be used in the field of medical container and thelike. Thus, the present invention is useful.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing one example of the mouth member.

FIG. 2 is a cross-sectional view of the A-frame part having a gap.

FIG. 3 is a cross-sectional view of the A-frame part in the case ofusing a mouth member where a thin strip is provided and extended.

FIG. 4A is a cross-sectional view showing the state where themelt-bonding part of the mouth member is preliminarily heated by anannular heater.

FIG. 4B is a cross-sectional view showing the state where a heatinsulating plate is provided and the melt-bonding part of the mouthmember is preliminarily heated by an annular heater.

FIG. 4C is a cross-sectional view cut along A-A in the cross-sectionalview of FIG. 4A.

FIG. 5A is a perspective view showing another example of the mouthmember.

FIG. 5B is a cross-sectional view of the another example of the mouthmember.

FIG. 6 is a cross-sectional view showing the state where the mouthmember and the bag unit are depressurized.

FIG. 7A is a horizontal cross-sectional view of a sealing mold.

FIG. 7B is a partially enlarged view of FIG. 7A.

FIG. 8 is a longitudinal cross-sectional view of a sealing mold.

FIG. 9 is a medical container by the bag-making method.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below by referring to thedrawings.

The mouth member 1 works out to an injection inlet/outlet of a bag andthe cross-section thereof has a hollow circular, elliptic, rhombic orboat form. Also, one mouth member may have a plurality of injectioninlets/outlets.

In the case where the mouth member 1 has a circular cross-section, thediameter is from 10 to 30 mm, the thickness of the mouth member is from0.5 to 3 mm and the height is approximately from 20 to 80 mm.

Examples of the synthetic resin used for the mouth member includepolyester resins such as polyethylene terephthalate and polybutyleneterephthalate, polycarbonate resins, and polyolefin-base resins such aspolypropylene and polyethylene. Among these, preferred arepolyolefin-base resins, more preferred is a single resin or a blendedresin of polyethylene-base resins such as high-density polyethylene,linear low-density polyethylene, high-pressure process low-densitypolyethylene and polyethylene produced by using a metallocene catalyst.The same resin as the flexible film constituting the bag unit ispreferably used.

The mouth member 1 may comprise multiple layers. In particular, it ispreferred that the same resin as the flexible film is used for theoutermost layer of the mouth member and a resin higher in the heatresistance and rigidity than the outer layer is used for the innermostlayer, because the mouth member is more suppressed from the deformationat the preliminary heating and at the same time, when an injectionneedle is erroneously pieced inside the mouth member, the needle isprevented from piercing from the inside to the outside on the sidesurface of the mouth member.

The bag unit 2 comprises a flexible film and examples of theconstruction material thereof include polyolefin resins such aspolypropylene and polyethylene, polyamide resins and polyester resins. Aconstruction material having a melting point approximated to that of themelt-bonding face 12 of the mouth member 1 or a polyolefin-base resinobtained by blending such resins is preferred. The flexible film mayhave either a single-layer structure or a multilayer structure and thethickness thereof is approximately from 100 to 400 μm. In the case of amultilayer laminate film, a construction material of the same resin asand approximated in the melting point to the melt-bonding face of themouth member or a resin obtained by blending such materials ispreferably used for the inner surface of the bag unit. For the flexiblefilm, a cylindrical film produced by inflation molding or a bag materialobtained by folding a film produced by T-die casting or the like orsuperposing the films is used.

In the bag-making method of the present invention, the melt-bonding isperformed after the mouth member 1 formed of a synthetic resin ispreliminarily heated. The mouth member 1 is produced by injectionmolding in almost all cases and the present inventors have found thatthe residual stress generated at the injection molding and confined inthe mouth member is released at the preliminary heating to deform themouth member and therefore, when the deformed mouth member 1 is pressedtogether with the bag unit 2 by a sealing mold 5, the contact with thefilm of the bag unit 2 becomes non-uniform, as a result, local contactor gap is generated between the mouth member 1 and the film of the bagunit 2 before the melt-bonding. More specifically, the relativepositional relationship among the mouth member 1, bag unit 2 and sealingmold 5 changes due to the deformation of the mouth member and theA-frame part gap cannot be filled with the mouth member resin in somecases. For constantly establishing a preferred refative positionalrelationship among the mouth member 1, bag unit 2 and sealing mold 5,the mouth member 1 should be prevented from deforming at the preliminaryheating. The present inventors have found that the deformation can beprevented by performing the preliminary heating without softening theend part 11 of the mouth member, as a result, the mouth member 1, bagunit 2 and sealing mold 5 can be adjusted to respective exact positionsand the bag unit 2 and mouth member 1 can be melt-bonded withoutgenerating an A-frame part gap.

Conventionally, the mouth member 1 and the bag unit 2 have beenmelt-bonded by defining the melt-bonding part of the mouth member to theportion of the mouth member excluding the upper part 13 of the mouthmember, to which a rubber plug is fixed, and heating the mouth memberuntil the melt-bonding part is softened. However, in order to suppressthe deformation of the mouth member 1, when the end part 11 in the bagside of the mouth member, which is an end part of mouth member as wellas the upper part 13 of the mouth member are not heated and thereby notsoftened, the mouth member as a whole is prevented from deforming, thepositional precision of the mouth member, bag unit and sealing mold isenhanced, the contact property is improved, uniform melt-bonding andformation of thin strips at the melt-bonding part of the mouth memberare realized and melt-bonding free of a gap in the A-frame part betweenthe bag unit and the mouth member can be achieved. According toconventional methods, the end part of the mouth member is also heatedand depending on the case, heated to a temperature higher than themelting point of film, as a result, thinning of film is readilygenerated in the vicinity of the end part of the mouth member at thesealing of the mouth member 1 and the bag unit 2. This problem can alsobe solved by the above-described technique. The partial thinning of filmis prevented and therefore, the bag falling strength of the containerbody is improved.

The “softening” as used herein means a state where the resin is softenedto such a degree that the surface of the melt-bonding part of the mouthmember pressed by a sealing mold through a film is melt-bonded to thefilm and at the same time, a thin strip is formed. The non-softened endpart of the mouth member is confirmed with an eye to have the samesurface state as the surface of the mouth member before the preliminaryheating. In this case, a clear boundary line is observed at the boundarybetween the end part of the mouth part and the melt-bonding part of themouth member before the pressing by a sealing mold. By preliminarilyheating the mouth member to provide a state that this boundary line isobserved with an eye, the object of the present invention can beachieved.

In the preliminary heating, direct heating by using a hot mold orheating by radiation heat from a heat source such as annular heater orfar infrared ray is employed and the surface temperature of themelt-bonding part 12 of the mouth member to the bag unit, which is amelt-bonding part of mouth member is set to a temperature where thesynthetic resin used for the mouth member is softened.

Among these heating methods, heating by radiation heat is advantageousin view of attachment of foreign matters and simplification of themachine structure and therefore, this method is preferred. For thepreheater 3, an annular heater having a shape of not heating the endpart 11 of the mouth member is preferably used. FIGS. 4A and 4B each isa cross-sectional view showing one example of the mouth member duringpreliminary heating with an annular heater 31 covered by 33 heatinsulating material. The clearance between the mouth member 1 and thepreheater 3 can also be maintained to a higher precision by fitting themouth member 1 at the non-heating part 34 of the annular heater orfitting a support into the hollow part of the mouth member 1 from theupper portion of FIGS. 4A and B, thereby supporting the mouth member atleast at two portions to keep the exact spatial arrangement of the mouthmember 1 and the annular heater. Furthermore, when the mouth member isrotated, the quantity of heat received from the preheater 3 can be madeuniform over the entire circumference of the melt-bonding part 12 of themouth member. When the quantity of heat applied to the melt-bonding part12 of the mouth member at the preliminary heating step is stabilized andhomogenized, the deformation of the mouth member 1 is more suppressedand the positional adjustment of the mouth body, bag unit and sealingmold can be more exactly performed.

The heating temperature must be a temperature sufficiently high to forma thin strip on the mouth member at the time of pressing the mouthmember through a film in the melt-bonding step. In the case of heatingby radiation heat, the heating temperature can be appropriately selectedaccording to the clearance between the heat source and the mouth membersurface, or the construction material of the mouth member, but theheating is preferably performed for 8 to 13 seconds by setting the heatsource at a temperature of 500 to 750° C., though this may varydepending on the construction material of the mouth member. If thetemperature of the melt-bonding part 12 of the mouth member is too high,a degraded product of synthetic resin may be generated or flowdeformation may occur and furthermore, the end part of the mouth membermay be softened due to the effect of the temperature at the melt-bondingpart of the mouth member, therefore, this must be avoided.

To speak specifically, in order to not soften the end part 11 of themouth member and soften the melt-bonding part 12 of the mouth member,the end part 11 of the mouth member is, for example, protruded by atleast 0.5 mm or more, preferably 0.8 mm or more, than the heat sourcesuch as annular heater, whereby the end part 11 of the mouth member caneffectively avoid being affected by the radiation heat and softened, asa result, the mouth member as a whole can be prevented from reduction inthe rigidity and deformation due to heat.

Other examples include, as shown in FIG. 4B, a method of using heatinsulating means such as heat insulating plate 32 for preventing the endpart 11 of the mouth member from being subjected to radiation heat froma heat source and, although not shown, a method of cooling the end partof the mouth member by abutting thereto a cooling mold having a circularcap-like recessed portion into which the end part of the mouth member isentered. Furthermore, the object of the present invention can also beachieved, as shown in FIGS. 5A and 5B, by using a mouth member where thediameter is reduced at the end part 11 of the mouth member in the regionin a length L of 5 mm or less, preferably from 1 to 5 mm, from thelowermost portion 14 of the mouth member so as to enlarge the distanceof the end part 11 of the mouth member from the heat source as comparedwith the melt-bonding part 12 of the mouth member.

The melt-bonding step of pressing and thereby melt-bonding the mouthmember and the bag unit is a step of inserting the preliminarily heatedmouth member into the opening of the bag unit and pressing them by asealing mold to melt-bond the melt-bonding part of the mouth member tothe opening. An example of the melt-bonding step is described below byreferring to FIG. 6. In the following example, a mouth member supportedby a cylindrical body is inserted into the opening of a bag unit and thebag unit is depressurized and is melt-bonded to the mouth member. Themethod by depressurization is more effective in the case where thediameter of the mouth member exceeds 10 mm. An analogous method isdescribed in Patent Document 6.

For facilitating the holding of the mouth member, as shown in FIG. 6, acylindrical body 4 is inserted into the hollow part of a hollowcylindrical mouth member 1.

The cylindrical body has an outer diameter slightly smaller than theinner diameter of the mouth member and in the inside thereof, a hole ispenetrated to the distal end. The distal end (air suction inlet 43) ofthe cylindrical body is formed to give a shape conforming to the bentfilm, that is, a shape where the sectional area gradually decreasestoward the distal end of the cylindrical body.

The sectional area starts gradually decreasing at the position 5 mm ormore from the distal end of the cylindrical body and at the same time,closer to the distal end than the end part 11 of the mouth member. Thecylindrical body is inserted such that the distal end 43 of thecylindrical body protrudes at least 5 mm or more from the end part 11 ofthe mouth member. The inside of the bag unit is depressurized bysuctioning air therein, which is described later, and thereby thecylindrical body 4 and the bag is more tightly contacted. Furthermore,if the cylindrical body 4 is served also as a fixing jig for the mouthmember 1 in the preliminary heating step, this may provide an effect ofmore preventing the deformation of the mouth member, however, since themachine structure is complicated, that is, the machine structure needsto be constituted by taking account of the difference between thesealing time (time period where the sealing mold is pressed) and thepreliminary heating time, the equipment is slightly complicated and thisgives rise to increase in the cost.

If desired, the inside of the bag unit is depressurized by suctioningair by the depressurization port 42 therein to enhance the tight contactbetween the cylindrical body 4 and the bag 2. The timing ofdepressurization is before the sealing mold 5 is secured orsimultaneously with the closing of the sealing mold 5. The bag unit isfixed by the depressurization and therefore, troubles such as thinningof film or generation of pinhole at the boundary between themelt-bonding part and the non-melt-bonding part due to the effect ofheat from the sealing mold 5 can be very efficiently prevented fromoccurring. Furthermore, the bag unit 2 and the mouth member 1 arestrongly contacted by the depressurization and therefore at thecylindrical support part 41, the film is bentand fixed in agreement withthe shape of the end part 11 of the mouth member. In addition, due tothe low temperature at the end part of the mouth member, the thinning isinhibited with good efficiency.

The bag unit 2 and the mouth member 1 are pressed by a sealing mold 5shown in FIG. 7 to melt-bond the melt-bonding part 12 of the mouthmember and the melt-bonding part 21 of the bag unit. The temperature ofthe sealing mold 5 is higher by 10° C. or more than the melting point offilm (bag unit resin) and in the case of a film formed of a polyethyleneresin, this temperature is from 110 to 170° C. and the melt-bonding timeis approximately from 1 to 3 seconds. The time period after thepreliminary heating until the pressing by the sealing mold 5 ispreferably as short as possible, but due to the limitation by theproduction apparatus, this time period is usually on the order of 1 to 4seconds. If this time period exceeds 4 seconds, the surface temperatureat the melt-bonding part of the mouth member decreases and the sealingstrength between the mouth member 1 and the bag unit 2 is liable to beinsufficient. At the melt-bonding, when the corner of the mold has asmall R as shown in FIG. 7B, a thin strip can be easily formed.

The sealing mold 5 has a shape comprising a semicircular cross-sectionand a flat part and R is formed at the connection part of thesemicircular cross-section and the flat part, that is, at the A-framepart between the mouth member 1 and the film. R is from 0.2 to 2 mm,preferably from 0.3 to 1.7 mm. If R is too large, formation of theA-frame part gap cannot be prevented, whereas if it is too small,troubles are readily generated, for example, the film is scratched or aninsufficient thin strip is formed. The diameter of the semicircularcross-section is slightly smaller than the size obtained by adding thefilm thickness to the diameter of the melt-bonding part 12 of the mouthmember. Also, the sealing mold 5 is preferably designed to perform themelt-bonding without heating the region at least 0.5 mm from thelowermost portion of the end part of the mouth member so that thinningof the film can be avoided. Examples of such a sealing mold 5 include amold having a shape such that the region in a length of at least 0.5 mmfrom the lowermost side of the end part of the mouth member iscontrolled to a temperature lower than the melting point of the film. Apreferred sealing mold is a mold of, as shown in FIG. 8, allowing themouth member 1 to protrude by a length of M from the sealing mold 5. Thelength M is preferably 0.5 mm or more. With this length, the film is notpressed between the distal end of the mouth member and the mold andthinning of the film is hard to occur. In this time, this film may bethe part of a medical container 6 shown in FIG. 9.

In this example, the mouth member and the bag unit are melt-bonded whilethe bag unit is depressurized, however, the effect of the presentinvention can also be achieved by softening the melt-bonding part 1 ofthe mouth part, where the mouth member 1 and the bag unit 2 aremelt-bonded, while preventing the end part 11 of the mouth member frombeing softened at the preliminary heating, and pressing the mouth member1 and the bag unit 2 without using a cylindrical body.

In the mouth member 1 heated at the preliminary heating step of thepresent invention, the residual stress generated at the injectionmolding is eliminated and the deformation is prevented, as a result, themouth member 1 and the bag unit 2 each can be fitted to the exactposition with respect to the sealing mold 5. Since these are melt-bondedin such an exactly positioned state, the softened resin in themelt-bonding part 12 of the mouth member pressed to the flexible filmforms a thin strip having a stable shape and extending in the A-framepart gap.

The thin strip suitably has a size such that the thickness isapproximately from 50 to 200 μm and the length is approximately from 0.1to 2 mm. According to the present invention, the mouth member comes tohave a thin strip of this size and by melt-bonding the mouth member, abag with a mouth member free from formation of A-frame part gap andgeneration of liquid leakage can be stably produced.

After the mouth member is melt-bonded, the melt-bonding part issandwiched by a cooling mold. Since the deformation of the mouth memberat the preliminary heating is prevented, similarly to the sandwiching bya sealing mold, the material to be sandwiched can be exactly and stablypositioned also at the sandwiching by a cooling mold and therefore, athin strip is stably molded.

In the case where the inside of the bag unit has been depressurized, thedepressurization is released. By performing the melt-bonding and coolingin the depressurized state, the film is tightly contacted and fixed inagreement with the shape of nozzle until the film is melt-bonded withthe mouth member by a film sealing mold and cooled. The melt-bonding isperformed as such in the state where the film is inhibited from freemovement, and this provides an effect that the melted and softened filmis not stretched and the film is not thinned at the boundary of themelt-bonding part and the non-melt-bonding part of the mouth member.

EXAMPLES

A mouth member formed of an equivalent blend composition of high-densitypolyethylene and linear low-density polyethylene and having a circularcross-sectional shape was produced by injection molding, where thediameter was 17 mm, the inner diameter was 13 mm and the thickness atthe melt-bonding part and the end part of the mouth member was 2 mm.

A tubular linear low-density polyethylene film having a width of 140 mmwas formed by inflation molding and cut into a length of 300 mm. One cutpart was closed by heat sealing and another cut part was used as themelt-bonding part of the opening. On the other hand, an annular heaterdesigned such that the surface temperature at the radiation part becomes700° C. and the end part of the mouth member protrudes by 1 mm from theradiation part was inserted into the mouth member while aligning thecenter with the center of the mouth member and heated for 10 seconds.After a hollow cylindrical body was fit into the mouth member, the mouthmember was swiftly inserted into the melt-boning part of the bag unitprepared above and simultaneously with suctioning by a vacuum pump todepressurize the inside of the bag unit, the melt-bonding part wassandwiched by a sealing mold set at 140° C. for 2 seconds. Subsequently,the melt-bonding part was sandwiched by a cooling mold for 3 seconds andafter the vacuum was relieved, the hollow cylindrical body was pulledout to produce a bag with a mouth member.

100 Units of this bag with a mouth member were prepared and afterfilling 500 mL of water into each bag and tightly plugging it, the bagwas externally pressed to give an internal pressure of 0.07 MPa and thenleft standing for 5 minutes. In all bags with a mouth member, waterleakage was not observed.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. A bag-making method for producing a bag by melt-bonding and therebyintegrating a mouth member formed of a preliminarily heated syntheticresin and a bag unit formed of a flexible film, said method comprising;a preliminary heating step of softening the synthetic resin of the mouthmember at the part to be melt-bonded to the bag unit, which is amelt-bonding part of mouth member, while preventing the synthetic resinof the mouth member at the end part in the bag side, which is an endpart of mouth member, from being softened at the preliminary heating,and a melt-bonding step of inserting the preliminarily heated mouthmember into the opening of the bag unit and pressing them by a sealingmold to melt-bond the melt-bonding part of the mouth member to theopening.
 2. The bag-making method as claimed in claim 1, whereinradiation heat is used for the preliminary heating.
 3. The bag-makingmethod as claimed in claim 1, wherein the end part of the mouth memberhas a length of 0.5 mm or more.
 4. The bag-making method as claimed inclaim 1, wherein the end part of the mouth member is prevented by heatinsulating means from being heated at the preliminary heating.
 5. Thebag-making method as claimed in claim 1, wherein in the melt-bondingstep, the melt-bonding is performed not to heat the mouth member in theregion at least 0.5 mm from the lowermost portion of the end part. 6.The bag-making method as claimed in claim 1, wherein a mouth membersupported by a cylindrical body is inserted into the opening of a bagunit and the mouth member and the bag unit are melt-bonded while the bagunit is depressurized.
 7. A medical container produced by the bag-makingmethod claimed in claim 1.